Electrodynamic loudspeaker



July 14, 1936 A. POGGENDORFF 2 O47 381 l ELECTRODYNAMI C LOUDSPEAKERFiled April l5, 1952 INVENTOR ADOLF POGGENDORFF ATTORNEY Patented July14, 1936 PAT-ENT orifice ELEcTRoDYNAMIc LoUnsrEAKER.

Adolf Poggendorff, Berlin-Weissensee, Germany,

assignor to Gesellschaft fr Drahtlose Telegraphie m. b. H., Berlin,Germany, a corporation of Germany Application April 13, 1932, Serial No.604,939 In Germany August 13, 1931 4 Claims.

'I'he invention relates to acoustic apparatus. More particularly, itrelates to acoustic apparatus of the electrodynamic or moving coil type.

In the operation of electrodynamic loudspeakers it has been found thatoccasionally the supply leads start to oscillate whenever they happen tobecome excited at their natural period. As a result of such vibrationsthe wires may break oir especially at the points where they are attachedto the diaphragm or at the terminals in the casing. The comparativelystout and therefore less yielding (more brittle) loudspeaker supplyleads whose driving element consists of. a single conductor or whosediaphragm is itself designed to act as the current supply element, areparticularly sensitive. The feed leads in this case must be made quiterugged since occasionally they have to carry currents up to amps.

In an attempt to obviate this drawback, it has previously been suggestedin the art to round olT the edges of the terminals, but this plan givesthe desired results only in a few instances.

According to the present invention the above diiiiculties are overcomeby articially damping the supply leads. The damping is eiected by theprovision of supplementary masses (lead cables) or by the action ofadditional damping elements upon the conductors. The additional dampingmaterial may be felt or rubber, or some similar substance insuring highdamping or deadening of vibrations, though the same effect might also beinsured electrically. Such supplementary masses cause a shift in thenatural period into a region where the exciting force is low. Since inthe movement of the conductors such supplementary masses are subjectedto deformation, this means the production of. energy consuming work; inother words, damping is thereby produced.

According to another object of the invention it will be found ofadvantage in the above scheme to provide some yielding material likerubber to be interposed at the point where the unsupported conductorpasses over into the binding post so that the clamping means will beable to yield whenever subjected to stress caused by vibrations.

The figures show embodiments of the basic idea of the invention, Fig. 1showing the ways and means to feed the currents to the voice coil of astandard plunger type coil loudspeaker. Fig. 2 shows a furtherembodiment of the basic idea of the invention.

In Fig. 1, the connection from the output of the amplier (not shown) is.eil'ected at the terminal board or plate I from which the leads 2 and 3are brought to the voice coil 4. The leads are each enveloped with asheath or cable ,f' of lead or rubber in which mineral powder has beenincorporated in order' to raise the damping. This causes an increase inthe mass which, in turn, exercises an influence upon the damping of the5 natural period.

In Fig. 2 there is illustrated schematically a loudspeaker of thedynamic type in which the current conducting element occasioning themechanical drive comprises a single conductor. In 10 such arrangementswhich are especially suited for large power loudspeakers, it isnecessary to provide rather stout supply leads to meet the demands ofthe electrical load. But, on the other hand, the supply leads should notbe chosen too 15 heavy since they would otherwise tend to undulyincrease the inert mass partaking of the oscillations, or else theymight impair the chances for free vibrations of the system because oftheir stiffness. Such supply leads possessing relative- 20 ly highbrittleness, as pointed out before, are very sensitive to an excitationof their mechanical natural period so that damping means must beprovided.

Fig. 2 shows an arrangement of. this kind. The 25 conductor 5 is clampedtogether with the terminal board 6 with rubber layers I being suitablyinterposed. The clamping is preferably made so firm that the dampingeiect of the rubber gets a chance to make itself felt. Rubber 30compounded with a. mineral powder is most suitable since such rubberevidences very high damping properties. The conductors 5, which arebrought unsupported from the terminals 6, are further supported betweenfelt pads or bodies 8. 35 Felt has different damping properties thanrubber so that the conductors are embedded orinterposed betweenmaterials having dissimilar effects. Other materials possessing asimilar action may be employed in lieu of rubber or felt.

What I claim is:

1. An electrodynamie loudspeaker having a vibratile system including avoice coil, a diaphragm connected with said voice coil, leads forsupplying energy to said voice coil, means on said and felt placedbetween said supply leads as they 55 ing a vibratile system including avoice coil, voice coil leads extending to xed points, said voice coilleads having natural periods of vibration and damping members in theform of lead cables surrounding said voice coil leads for effectivelydamping the vibrations of said leads at the frequencies oi their naturalperiods.

ADOLF POGGENDORFF.

